1. Field of the Invention
The present invention relates to an offshore marine construction method and apparatus for transporting and erecting marine superstructures on marine structures within a body of water such as for example, a river, lake, sea or ocean.
More particularly the invention relates to an improved and efficient method of setting large marine superstructures on marine structures or offshore towers. The marine superstructure in most cases would be used as a platform to support a drilling apparatus or a petroleum production plant. The marine superstructure could also be a platform to support a radar or sonar devise, a helicopter refueling station, a pumping station or a light house.
This invention is also an improved and efficient method of removing marine superstructures from marine structures and transporting the marine superstructure to shore.
2. Description of Prior Art
A derrick barge or crane whip is a well used tool for assisting in the construction of marine structures and superstructures. However, its lifting ability is limited by the height of the superstructure to be lifted, and the horizontal distance from the derrick to the center of the superstructure combined with the weight of the superstructure.
As the weight, size and height of the marine superstructure is increased, the size of the derrick must be increased at an exponential rate, or the marine superstructure must be fabricated in sections and assembled offshore; either solution is very expensive.
To increase the weight lifting ability of a derrick barge, the boom must be made heavier, the cables must be a greater diameter and the number of cables must be increased, a more powerful and heavier winch must also be added. With the increased weight of the cables, boom, winch and other machinery added above the main deck of the vessel, the center of gravity is elevated and the vessel may become unstable; to compensate for this instability the size of the vessel will most likely have to be increased. Again the cost of the derrick barge will be increased exponentially.
A major problem with a derrick barge or a crane ship is that when the sea conditions are not calm or near calm, the derrick barge or the crane ship must stop working. The reason why work must stop is that a wave may cause the barge or ship to move only one foot in any direction; that one foot of motion could translate into two or three feet of motion in the derrick itself and two or three feet of motion could translate into eight or ten feet of motion at the end of the boom.
When lifting a heavy marine superstructure any motion at all will add a massive amount of stress to the derrick and could possibly cause it to fail.
The semi submersible derrick vessel is another offshore construction tool for lifting marine structures and marine superstructures.
The semi submersible derrick vessel is a column stabilized vessel with four or more columns and with one, but more often two, large derricks mounted over two of the four columns. This vessel operates in much the same manner as derrick barge or crane ship except that it is affected less by waves.
The semi submersible derrick vessel has the same problems with the derrick as does the derrick barge. To be capable of lifting over the top of a marine structure the boom, cables, winches and other machinery must be quite heavy and therefore increase the cost of the total unit.
Another problem with a semi submersible derrick vessel is that it is towed on two or more pontoons which is difficult and costly; it is also very unstable with the weight of the upper hull and the one or two derricks well over a hundred feet above the pontoons.
A semi submersible derrick vessel is far more expensive than a derrick barge or a crane ship but it has an advantage of being able to work in more severe wave conditions.
Another major problem with any vessel that requires a crane or a derrick is that the lifting must be done from above the marine superstructure. To lift from above, pad eyes must be installed above the structure and the pad eyes must be suitably fastened to the main structure which is usually the lower part of the marine superstructure.
The most efficient method of lifting an object is to grasp the object from underneath. To lift a table, chair, desk, refrigerator, automobile or most other objects the most common, efficient and time proven method is to lift from under the object. Derrick or crane vessels only lift a marine superstructure from above which is inefficient and more expensive.
When using a derrick barge, crane ship or a semi submersible derrick vessel another vessel called a deck cargo barge or a launch barge must also be used to transport the marine superstructure. This second barge will also require the services of at least two tug boats and an anchor laying vessel which will further increase the cost of setting a marine superstructure onto a marine structure.
It would be more desirable to transport a marine superstructure and a small semi submersible vessel on a single barge hull. Additionally, it would be an advantage to lift a marine superstructure from underneath on its main beams. Further, it would be a greater advantage to be capable of lifting a greater load at a lower cost.
Several types of lifting devices have been known and used before and typical examples thereof are shown in U.S. Pat. No. 2,592,448 issued Apr. 8, 1952 to W. V. McMenimen; U.S. Pat. No. 2,907,172 issued Oct. 6, 1959 to W. S. Crake; French Patent No. 1.214.760 E. 21B issued Apr. 12, 1960 to N. V. De Bataafsche; U.S. Pat. No. 2,959,015 issued Nov. 8, 1960 to Robert W. Beck; U.S. Pat. No. 3,054,267 issued Sept. 18, 1962 to I. W. Alcorn et al; U.S. Pat. No. 3,183,676 issued May 18, 1965 to R. G. LeTourneau; U.S. Pat. No. 3,442,340 issued May 6, 1969 to L. B. Christenson; U.S. Pat. No. 3,727,414 issued Apr. 17, 1973 to P. Davies; U.S. Pat. No. 3,442,340 issued Aug. 16, 1977 to V. E. Lucas; U.S. Pat. No. 4,045,967 issued Sept. 6, 1977 to J. F. Schirtzinger; U.S. Pat. No. 4,224,005 issued Sept. 23, 1980 to E. D. Dysarz; U.S. Pat. No. 4,651,667 issued Mar. 24, 1987 to deBoer et al; None of these devices, however, teach the transportation of a semi submersible and a marine superstructure on a single barge, the placing of the marine superstructure onto the semi submersible vessel, further elevating the semi submersible vessel while efficiently supporting the marine superstructure underneath and further setting the marine superstructure on a marine structure.